Method and apparatus for determining the depth of submerged lances and the like

ABSTRACT

Method and apparatus for determining the depth of a submerged article with the use of a pressure probe, and in particular the depth of a submerged lance used to deliver a gaseous reaction agent to a metallic bath. The probe is adjacent or within a conduit delivering the gaseous reaction agent to the bath. The pressure at the probe is compared with that above the bath, the difference between the two pressures being proportional to depth. The system can be used in installations where the pressure at the surface of the bath is atmospheric pressure or in cases where the space above the surface is evacuated as in vacuum decarburization of stainless steels and the like. In the former case, the probe is usually pressurized to prevent clogging of the tip. In the latter case, the ambient pressure at the tip of the probe is compared with that above the surface of the bath and the probe pulse-pressurized periodically to prevent clogging.

United States Patent [191 Acre et al.

[ METHOD AND APPARATUS FOR DETERMINING THE DEPTH 0F SUBMERGED LANCES ANDTHE LIKE [75] Inventors: Thomas R. Acre, New Kensington,

Pa.; Frederick M. Gimbel, Kokomo,

lnd.; Sundaresan Ramacheandran, Natrona Heights, Pa.

[73] Assignee: Allegheny Ludlum Industries, Inc.,

Pittsburgh, Pa.

[22] Filed: Aug. 18, 1971 [21] Appl. No.: 172,697

14 1 Dec. 25, 1973 Primary Examiner-Richard C. Queisser AssistantExaminer-Denis E. Corr Attorney-Vincent G. Gioia et al.

[ 5 7 ABSTRACT Method and apparatus for determining the depth of asubmerged article with the use of a pressure probe, and in particularthe depth of a submerged lance used to deliver a gaseous reaction agentto a metallic bath. The probe is adjacent or within a conduit deliveringthe gaseous reaction agent to the bath. The pressure at the probe iscompared with that above the bath, the difference between the twopressures being propor- 52 us. 01. 73/302 tional dePth- The System canbe used in installatms [51] Int CL G0 23/14 where the pressure at thesurface of the bath is atmo- [58] Field of Search 73/302 301' sPericPmure in cases where the 266/34 L, 2 surface is evacuated as in vacuumdecarburization of stainless steels and the like. In the former case,the [56] References Cited probe is usually pressurized to preventclogging of the UNITED STATES PATENTS tip. In the latter case, theambient pressure at the tip of the probe is compared with that above thesurface ,47,t23g(2) 9/1947 Peterson 1. 73/302 f the bath and the probepulse pressurized i 4 2 3x328 cally to prevent clogging. 1,359,01411/1920 Alexander 73/302 3 Claims, 6 Drawing Figures PRESSUR/ZED 6A5 '40sou/m5 45 PRESSURE 04s PRESSURE SOURCE REGULATOR l l PULS/NG MECHANISM{mm-cm: TORI GAS SOURCE PULS/NG PRESSUfl/ZED GAS SOURCE VOL. FLOW RA TEMECHAN/SM SHEET 2 0F 2 PAIENTEU was ma 6. 76* AT CONSTANT 1 METHOD ANDAPPARATUS FOR DETERMINING THE DEPTH OF SUBMERGED LANCES AND THE LIKEBACKGROUND OF THE INVENTION As is known, many metallurgical processesrequire the introduction of a gas onto the surface or within a volume ofmolten metal for the purpose of reacting impurity elements in the meltwith the gas phase to form volatile reaction products Desiliconization,degassing and decarburization are some of the processes that employ sucha technique. In the basic oxygen process (BOF), the refining oxygen isintroduced in the form of a jet issuing from a lance positioned abovethe surface of the bath. The interaction of the oxygen jet with theliquid metal results in the'oxidation of carbon and other elementscapable of chemically reacting with the oxidizing gas. However, blowingoxygen or another gaseous reaction agent onto the surface of a moltenmetal bath results in considerable splashing and slopping of liquid inthe vessel and undesirable oxidation of useful alloying elements.

For minimum splashing, the lance tip of a gas injection lance should beimmersed in the metal bath. Furthermore, the depth of immersion iscritical. When the lance is one inch or more above the bath or isimmersed inches or more, splashing and slopping of the metal bath arenoticeably increased. Furthermore, when the lance tip is immersed morethan six inches below the liquid level of the metal bath, severe erosionof the lance occurs. The desired depth of the lance tip is preferably nogreater than two inches.

SUMMARY OF THE INVENTION In accordance with the present invention, amethod and apparatus are provided for determining the depth of thebottom of a gas lance in a molten metal bath by providing a conduit orprobe having a tip terminating at the bottom of the lance and bymeasuring the pressure difference between that in the probe and thepressure above the surface of the molten metal bath. Specifically, thereis provided a conduit having a lower tip essentially coincident with thebottom of a gas-issuing lance in a molten metal bath and manometer meansfor comparing the pressure in the conduit with the pressure of theatmosphere above the surface of the bath whereby the depth of the lowertip and the bottom of the lance can be determined from a considerationof the difference in pressures in the conduit and above the surface ofthe bath. The pressure differential is the true measure of the depth ofimmersion of the bottom of the lance since the pressure within theaforesaid conduit adjacent the lance varies as a function of thehydrostatic pressure of the molten metal at the tip of the conduit orprobe.

It may happen that the tip of the probe, while the lance is immersed,will become clogged because of solidification of molten metal in thetip. This can be alleviated by pressurizing the probe itself; and thisis entirely acceptable in a case where the gas above the level of themolten metal bath is air at atmospheric pressure. However, in a vacuumdecarburization process wherein the space above the molten metal bath isevacuated, it has been found that the pressure within the evacuatedspace will vary, possibly due to the fact that there is an unevenevolution of gases from the melt. For this-reason, it is necessary topressurize the probe at a constant volumetric flow rate or otherwisepulse-pressurize the probe periodically in order to prevent clogging ofthe probe tip. While the depth reading will be disrupted during thepulse-pressurization, the system will immediately return to steady-stateconditions after each pulse in order that the depth can be determined.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIG. 1 is a schematic illustration of one embodiment of the inventionwherein the gas above the surface of a metallic bath is at atmosphericpressure;

FIG. 2 is a cross-sectional view of the lance shown in FIG. 1, takensubstantially along line IIII of FIG. 1;

FIGS. 3 and 4 are cross-sectional views, similar to that of FIG. 2,showing alternative embodiments of the lance construction of theinvention;

FIG. 5 is a plot showing the manner in which pressure differentialvaries as depth increases; and

FIG. 6 is a schematic illustration of an embodiment of the invention asapplied to vacuum decarburization apparatus.

With reference now to the drawings, and particularly to FIG. 1, there isshown a reaction vessel 10 comprising an outer metallic lining 12provided on its interior surface with a refractory lining 14. Within thevessel 10 is a bath 16 of molten metal, such as steel, covered with aslag layer 17. The vessel 10 has an open upper end 18 which receives agas-delivery lance 20, As shown, the lance 20 comprises a metallic pipeor tube 22, the lower portion of which is surrounded by a refractoryjacket 24. Passing through the wall of the pipe 22 is a second conduit26 connected to or integral with a probe 28 which extends downwardlythrough the pipe 22 and has a lower tip 30 coplanar with and terminatingat the bottom 32 of the lance 20. If the lance 20 is consumable, theprobe 28 should be made of similar material as the consumingportion sothat the probe consumes at about the same rate. If the lance isnonconsumable, the probe should also be non-consumable. Normally, boththe pipe 22 and the probe 28 will be formed from steel. It has beenfound from actual trials that the probe is preferably positionedadjacent and in abutment with the inside wall of the pipe 22 as shown inFIG. 2. With this arrangement, the pipe 22 will burn back or be consumedat about the same rate as the probe 28, thereby insuring that the bottomor tip of the probe 28 will be coplanar with the bottom of the lance 20at all times.

Alternative embodiments of the lance 20, while not preferred, are shownin FIGS. 3 and 4. In FIG. 3, the probe 28' is concentric with the pipe22' which is surrounded by a refractory jacket 24'. In FIG. 4, the probe28" is imbedded within the refractory jacket 24" surrounding the maingas delivery pipe 22". The arrangements of FIGS. 3 and 4, whileworkable, are not considered to be as reliable as the arrangement shownin FIG. 2 for insuring that the probe will burn back or be consumed atthe same rate as the main gas delivery conduit, such as pipe-22.

The upper end of the main gas delivery pipe 22 is connected to a sourceof gas under pressure. For purposes of illustration, it will be assumedthat this gas is oxygen which is used to burn out carbon and otherimpurities within the melt 16. For maximum effectivemess, the lance tipor bottom 32 should be immersed within the molten metal bath 16; howeverthe depth of immersion is critical. Rapid erosion of the lance occurswhen the tip is six inches or more beneath the level of the bath.Minimum splashing and slopping occur without incurring excessive erosionwhen the lance is no more than about two inches beneath the surface.

It is, of course, necessary to provide some means for determining whenthe bottom of the lance is at the desired depth; and this is complicatedby the fact that the lance will erode as mentioned above. Accordingly,the probe 28 within the pipe 22 is connected through conduit 26 andvalve 36 to one side of a manometer 38. The other side of the manometer38 is open to the atmosphere. Consequently, it is at the same pressureas the air above the surface of the molten metal bath l6.

Notwithstanding the fact that a violent chemical reaction occurs beneaththe bottom of the lance when oxygen is delivered into the molten metalbath l6, and notwithstanding the fact that the pressure at the lower endof the probe 28 is that of the oxygen passing through the pipe 22, ithas been found that the difference between the pressure at the probe tipand atmospheric pressure is an indication of the depth of the bottom ofthe lance 20. Thus, by observing the differential levels in themanometer 38, the depth of the bottom of the lance can be determined.

In the preceding discussion, it was assumed that the probe 28 was notconnected to an external source of pressure and that the pressure withinthe'probe was that at the bottom of the pipe 22. When the probe is notpressurized in this way, it is possible for molten metal to cling to theprobe tip 30 and possibly solidify, in which case the probe will beblocked. In order to prevent this condition, the probe itself can bepressurized. Thus, a pressurized gas source 40 can be connected througha pressure regulator 42 and valve 44 to the conduit 26. The gas fromsource 40 is preferably an inert gas; however air or even oxygen can beused. With the probe pressurized, the differential pressure readingobserved with the manometer 38 will be greater than i in the case wherethe probe is not pressurized; however the pressure differential 'isstill proportional to the depth of the bottom of the lance; and themanometer 38 can be calibrated to show this depth.

Instead of constantly pressurizing the probe, it is also possible topulse-pressurize it. In this latter case, a pressurized gas source 45 isconnected through a valve 46 to the probe 28, the valve 46 beingintermittently opened and closed by means of a pulsing mechanism 48. Thepulsed gas can then be made to flow into the conduit 26 through valve50, with valve 44 closed and valve 36 open. In this case, the pressuredifferential observed on the manometer 38 will be that between thepressure within the pipe 22 and atmospheric pressure,

except when a pulse of pressurized gas is introduced via valve 50. Apulse will be applied to the probe, for example, only once every minutesuch that a reading on the manometer 38 between pulses can bedetermined.

Instead of using the manometer 38, it is possible to close valve 36 andopen valve 52, in which case the conduit 26 is connected to adifferential pressure cell 54 which produces an output signal on lead 56proportional to the difference in pressure between that in probe 28 andatmospheric pressure. As will be understood, splashing and slopping ofthe molten metal bath will cause a variation in pressure within theprobe 28.

This results in a more or less continual movement of the mercury in themanometer 38, assuming that valve 36 is open. However, even with thiscontinual movement, it is possible to obtain a positive indication ofthe immersed depth of the lance by obtaining an average scale reading onthe manometer. This average scale reading can be obtained automaticallyby applying the output of the differential pressure cell 54 to anintegrator 58, the output of the integrator 58 being fed to a meter 60which indicates depth directly. In many cases, it is desirable to useboth the manometer and the electrical differential pressure cell. Thedifferential pressure cell can be used to generate an electrical signalwhose average magnitude represents depth as indicated on the meter 60,for example, while the movement of the mercury in the manometer 38 actsas an excellent indicator of the splashing and slopping of the bathduring injection. Since the manometer 38 and differential pressure cellcan be used interchangeably, the term manometer means" as used in theclaims herein means either.

A plot of pressure differential versus depth immersion is shown in FIG.5. Thus, when the end of the lance is in the gaseous atmosphere abovethe level of the molten metal bath, the pressure differential isrelatively low. When the bottom of the lance enters and passes throughthe slag layer 17, the pressure increases along a straight line.Finally, when the tip or bottom of the lance is immersed in the metalbath, the pressure differential rises linearly as depth increases, butat a much higher rate than when passing'through slag, which is of lowerdensity.

With reference now to FIG. 6, another embodiment of the invention isshown as. applied to vacuum decarburization. A molten metal bath 62 isagain positioned within a refractory-lined vessel 64. However, in thiscase, the vessel 64 is provided with a dome-shaped cover 66 connected tothe vessel 64 through an annular sealing arrangement 68. The dome-shapedcover 66, in turn, is connected through conduit 70 to an evacuatingpump, not shown, such that the space above the liquid metal bath 62 willbe evacuated. Vacuum decarburization of this type is employed in certaincases, particularly with stainless steels and the like, since theactivity of carbon (i.e., the rate at which it combines with oxygen toform carbon monoxide) is inversely proportional to the pressure abovethey bath. Hence, by evacuating the area above the bath, the refiningoxygen passing through the lance 20 preferentially combines with carbonrather than with chromium or other desired alloying constituents.

The lance in the embodiment of FIG. 6 is essentially the same as thatshown in FIG. 1 and, accordingly, elements of FIG. 6 which correspond tothose of FIG. 1 are identified by like reference numerals. In this case,however, the pipe 22 passes upwardly through a seal 72 in thedome-shaped cover 66. The conduit 26 is again connected to one end of amanometer 38; however in this case the other side of the manometer isconnected through conduit 74 to the evacuated space above the bath 62.

Unlike atmospheric pressure, the pressure above the bath 62 in theembodiment of FIG. 6 will vary due to the evolution of gases and/orsplashing and slopping of the metal bath. If the probe 28 is to beconstantly pressurized, therefore, it will be necessary to supply itwith a source of gas 76 me constant volumetric flow rate.

This source of gas can be connected to conduit 26, for example, throughvalve 78. Alternatively, it is possible to use the pulsing techniqueexplained above in connection with FIG. 1. In this latter case, valve 80will be open and valve 78 closed. Pressurized gas from gas source 82then passes through pulsing valve 84 connected to pulsing mechanism 86and thence through valve 80 to the conduit 26. Again, the probe need bepulsed only about once every minute. Thus, an average reading of themanometer 38 can be derived to determine the depth of the lance.Alternatively, the differential pressure cell 54 of FIG. 1 can be usedtogether with an averaging or integrating circuit in a direct read-outmeter, such as meter 60.

Although the invention has been shown in connection with certainspecific embodiments, it will be readily apparent to those skilled inthe art that various changes in form and arrangement of parts may bemade to suit requirements without departing from the spirit and scope ofthe invention.

We claim as our invention:

1. In combination, a gas-issuing lance immersed in a molten metal bath,means for forcing a gas through said lance and into the molten metalbath, a conduit having a lower tip essentially coincident with thebottom of said lance when immersed in a molten metal bath and subjectedto the pressure of the gas passing through the lance at the tip of thelance when it is so immersed, a source of gas under pressure, means forintermittently connecting said source of gas under pressure to saidconduit whereby the conduit is continually pulsepressurized, andmanometer means for comparing the pressure in said conduit with thepressure of gas above the surface of said bath while said conduit iscontinually pulse-pressurized whereby the depth of said lower tip andthe bottom of said lance can be determined from a consideration of thedifference in pressures in the conduit and above the surface of thebath.

2. In combination, a gas-issuing lance immersed in a molten metal bath,means for forcing a gas through said lance and into the molten metalbath, a conduit having a lower tip essentially coincident with thebottom of said lance when immersed in a molten metal bath and subjectedto the pressure of the gas passing through the lance at the tip of thelance when it is so immersed, manometer means for comparing the pressurein said conduit with the pressure of gas above the surface of said bathwhereby the depth of said lower tip and the bottom of said lance can bedetermined from a consideration of the difference in pressures in theconduit and above the surface of the bath, said manometer meansincluding a differential pressure cell for producing an electricaloutput signal proportional to the difference in pressure between that insaid conduit and the pressure above said surface of the bath, means forintegrating said electrical signal, and meter means connected to saidintegrating means for indicating said difference in pressure.

3. In combination, a gas-issuing lance immersed in a molten metal bath,means for forcing a gas through said lance and into the molten metalbath, a conduit having a lower tip essentially coincident with thebottom of said lance when immersed in a molten metal bath and subjectedto the pressure of the gas passing through the lance at the tip of thelance when it is so immersed, said lance and said conduit both beingconsumable in the molten metal bath, the conduit being positionedadjacent and in abutment with the inside wall of said lance whereby theconduit and lance will be consumed in the molten metal bath atsubstantially the same rate, and manometer means for comparing thepressure in said conduit with the pressure of gas above the surface ofsaid bath whereby the depth of said lower tip and the bottom of saidlance can be determined from a consid eration of the difference inpressures in the conduit and above the surface of the bath.

1. In combination, a gas-issuing lance immersed in a molten metal bath,means for forcing a gas through said lance and into the molten metalbath, a conduit having a lower tip essentially coincident with thebottom of said lance when immersed in a molten metal bath and subjectedto the pressure of the gas passing through the lance at the tip of thelance when it is so immersed, a source of gas under pressure, means forintermittently connecting said source of gas under pressure to saidconduit whereby the conduit is continually pulsepressurized, andmanometer means for comparing the pressure in said conduit with thepressure of gas above the surface of said bath while said conduit iscontinually pulse-pressurized whereby the depth of said lower tip andthe bottom of said lance can be determined from a consideration of thedifference in pressures in the conduit and above the surface of thebath.
 2. In combination, a gas-issuing lance immersed in a molten metalbath, means for forcing a gas through said lance and into the moltenmetal bath, a conduit having a lower tip essentially coincident with thebottom of said lance when immersed in a molten metal bath and subjectedto the pressure of the gas passing through the lance at the tip of thelance when it is so immersed, manometer means for comparing the pressurein said conduit with the pressure of gas above the surface of said bathwhereby the depth of said lower tip and the bottom of said lance can bedetermined from a consideration of the difference in pressures in theconduit and above the surface of the bath, said manometer meansincluding a differential pressure cell for producing an electricaloutput signal proportional to the difference in pressure between that insaid conduit and the pressure above said surface of the bath, means forintegrating said electrical signal, and meter means connected to saidintegrating means for indicating said difference in pressure.
 3. Incombination, a gas-issuing lance immersed in a molten metal bath, meansfor forcing a gas through said lance and into the molten metal bath, aconduit having a lower tip essentially coincident with the bottom ofsaid lance when immersed in a molten metal bath and subjected to thepressure of the gas passing through the lance at the tip of the lancewhen it is so immersed, said lance and said conduit both beingconsumable in the molten metal bath, the conduit being positionedadjacent and in abutment with the inside wall of said lance whereby theconduit and lance will be consumed in the molten metal bath atsubstantially the same rate, and manometer means for comparing thepressure in said conduit with the pressure of gas above the surface ofsaid bath whereby the depth of said lower tip and the bottom of saidlance can be determined from a consideration of the difference inpressures in the conduit and above the surface of the bath.